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Träfflista för sökning "L773:1094 4087 ;pers:(Hajdu Janos)"

Sökning: L773:1094 4087 > Hajdu Janos

  • Resultat 1-8 av 8
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1.
  • Andreasson, Jakob, et al. (författare)
  • Automated identification and classification of single particle serial femtosecond X-ray diffraction data
  • 2014
  • Ingår i: Optics Express. - 1094-4087. ; 22:3, s. 2497-2510
  • Tidskriftsartikel (refereegranskat)abstract
    • The first hard X-ray laser, the Linac Coherent Light Source (LCLS), produces 120 shots per second. Particles injected into the X-ray beam are hit randomly and in unknown orientations by the extremely intense X-ray pulses, where the femtosecond-duration X-ray pulses diffract from the sample before the particle structure is significantly changed even though the sample is ultimately destroyed by the deposited X-ray energy. Single particle X-ray diffraction experiments generate data at the FEL repetition rate, resulting in more than 400,000 detector readouts in an hour, the data stream during an experiment contains blank frames mixed with hits on single particles, clusters and contaminants. The diffraction signal is generally weak and it is superimposed on a low but continually fluctuating background signal, originating from photon noise in the beam line and electronic noise from the detector. Meanwhile, explosion of the sample creates fragments with a characteristic signature. Here, we describe methods based on rapid image analysis combined with ion Time-of-Flight (ToF) spectroscopy of the fragments to achieve an efficient, automated and unsupervised sorting of diffraction data. The studies described here form a basis for the development of real-time frame rejection methods, e. g. for the European XFEL, which is expected to produce 100 million pulses per hour. (C)2014 Optical Society of America
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2.
  • Aquila, Andrew, et al. (författare)
  • Time-resolved protein nanocrystallography using an X-ray free-electron laser
  • 2012
  • Ingår i: Optics Express. - 1094-4087. ; 20:3, s. 2706-2716
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 µs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
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3.
  • Chalupsky, J., et al. (författare)
  • Characteristics of focused soft X-ray free-electron laser beam determined by ablation of organic molecular solids
  • 2007
  • Ingår i: Optics Express. - 1094-4087. ; 15:10, s. 6036-6043
  • Tidskriftsartikel (refereegranskat)abstract
    • A linear accelerator based source of coherent radiation, FLASH (Free-electron LASer in Hamburg) provides ultra-intense femtosecond radiation pulses at wavelengths from the extreme ultraviolet (XUV; lambda< 100nm) to the soft X-ray (SXR; lambda<30nm) spectral regions. 25-fs pulses of 32-nm FLASH radiation were used to determine the ablation parameters of PMMA - poly ( methyl methacrylate). Under these irradiation conditions the attenuation length and ablation threshold were found to be (56.9 +/- 7.5) nm and similar to 2 mJ center dot cm(-2), respectively. For a second wavelength of 21.7 nm, the PMMA ablation was utilized to image the transverse intensity distribution within the focused beam at mu m resolution by a method developed here.
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4.
  • Ge, X., et al. (författare)
  • Impact of wave front and coherence optimization in coherent diffractive imaging
  • 2013
  • Ingår i: Optics Express. - 1094-4087. ; 21:9, s. 11441-11447
  • Tidskriftsartikel (refereegranskat)abstract
    • We present single shot nanoscale imaging using a table-top femtosecond soft X-ray laser harmonic source at a wavelength of 32 nm. We show that the phase retrieval process in coherent diffractive imaging critically depends on beam quality. Coherence and image fidelity are measured from single-shot coherent diffraction patterns of isolated nano-patterned slits. Impact of flux, wave front and coherence of the soft X-ray beam on the phase retrieval process and the image quality are discussed. After beam improvements, a final image reconstruction is presented with a spatial resolution of 78 nm (half period) in a single 20 fs laser harmonic shot. 
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5.
  • Glownia, James M., et al. (författare)
  • Time-resolved pump-probe experiments at the LCLS
  • 2010
  • Ingår i: Optics Express. - 1094-4087. ; 18:17, s. 17620-17630
  • Tidskriftsartikel (refereegranskat)abstract
    • The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.
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6.
  • Nelson, A. J., et al. (författare)
  • Soft x-ray free electron laser microfocus for exploring matter under extreme conditions
  • 2009
  • Ingår i: Optics Express. - 1094-4087. ; 17:20, s. 18271-18278
  • Tidskriftsartikel (refereegranskat)abstract
    • We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 mu J, 5Hz) using a fine polished off-axis parabola having a focal length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) -PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of <= 1 mu m. Observations were correlated with simulations of best focus to provide further relevant information.
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7.
  • Rath, Asawari D., et al. (författare)
  • Explosion dynamics of sucrose nanospheres monitored by time of flight spectrometry and coherent diffractive imaging at the split-and-delay beam line of the FLASH soft X-ray laser
  • 2014
  • Ingår i: Optics Express. - 1094-4087. ; 22:23, s. 28914-28925
  • Tidskriftsartikel (refereegranskat)abstract
    • We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 1016 W/cm2 with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.
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8.
  • Yoon, Chun Hong, et al. (författare)
  • Unsupervised classification of single-particle X-ray diffraction snapshots by spectral clustering
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:17, s. 16542-16549
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-particle experiments using X-ray Free Electron Lasers produce more than 10(5) snapshots per hour, consisting of an admixture of blank shots (no particle intercepted), and exposures of one or more particles. Experimental data sets also often contain unintentional contamination with different species. We present an unsupervised method able to sort experimental snapshots without recourse to templates, specific noise models, or user-directed learning. The results show 90% agreement with manual classification.
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  • Resultat 1-8 av 8

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